SpamAssassin is an email filtering system which identifies messages based on the content of the email header and body. It will help you in rejecting unwanted and unsolicited mails. You can enable it by following the steps mentioned below

1. Login to your cPanel
2. Under the Email section select Apache SpamAssassin

3. Click on Enable Apache SpamAssassin

4. You will then see a message confirming it has been enabled.

5. You will now want to enable the Spam Box.  This will ensure all emails marked as spam will go into a seperate folder labeled 'Spam', you will want to periodically go through and empty this out after ensuring all emails are spam. Click Enable Spam Box 

6. You are all set.  Once your first email that is marked as spam comes through, you will notice a new folder labeled Spam. **If for some reason you do not, you will want to make sure you are subscribed to that folder.**